This is a Mamiya Lens Hood for their 645AF 80mm f/2.8 Auto Focus Lens. It blocks stray light to prevent flare, and also provides some added protection against impact in case you get too close to your subject. It has a bayonet-type mount and features a 72mm diameter. It is included with the lens and offered here as a spare or replacement part. The hood will also work with other select lenses as specified in the list below. All of these lenses also include hoods as standard accessories.
Mamiya 645AF 80mm f/2.8 AF, SEKOR AF 55mm f/2.8 LS D, SEKOR AF 80mm f/2.8 LS D, SEKOR AF 110mm f/2.8 LS D, SEKOR AF 110mm f/2.8 LS D, SEKOR AF 150mm f/3.5 LS D